A man walks out of Samsung Electronics' headquarters in Seoul January 6, 2014.

Reuters/Kim Hong-Ji

SEOUL (Reuters) - Samsung Electronics Co Ltd on Thursday said it is investigating an allegation that a supplier in southern China used child labor.

U.S. activist group China Labor Watch on Thursday released a report alleging that Dongguan Shinyang Electronic Co Ltd, a supplier of mobile phone covers and parts, hired child labor for its assembly lines.

"We are urgently looking into the latest allegations and will take appropriate measures in accordance with our policies to prevent any cases of child labor in our suppliers," Samsung said an emailed statement.

Several phone calls to the Chinese company went unanswered.

The claim from the New York-based watchdog comes after Samsung said in an annual sustainability report on June 30 that a third-party audit of 100 suppliers in China found no instances of child labor.

On Thursday, Samsung said it conducted a "thorough audit" of Dongguan Shinyang in March 2013, followed by a third-party inspection in August and another last month.

"No cases of child labor were found during these audits," the South Korean firm said in its emailed statement.

Samsung demands suppliers adopt a hiring process that includes face-to-face interviews and the use of electronic scanners to detect fake IDs, to ensure compliance with Samsung's zero-tolerance policy on child labor.

But China Labor Watch said it found "at least five child workers" without contracts at the supplier in question.

"Samsung has put its energy into audits and the production of these reports, but these things are meant to appease investors and don't have any real value for workers," Li said.

The watchdog previously accused one of Samsung's suppliers of using child labor in 2012. Samsung subsequently said it found no under-aged workers at the facility following its own audit. (reut.rs/TUrmIo)

(Reporting by Se Young Lee; Additional reporting by Sui-Lee Wee in Beijing; Editing by Tony Munroe and Christopher Cushing)